Dual mode pilot director light utilizing visible and infrared light emitting diodes (LEDS)

ABSTRACT

Pilot Director Lights (PDLs) mounted on the exterior of a refueling tanker aircraft utilize visible light emitting diodes (LEDs) and infrared LEDs as light sources to provide visual information to the pilot of an approaching aircraft The PDLs are switchable between a visible mode that uses the visible LEDs and a covert mode that uses the infrared LEDs. The PDLs may include a plurality of light emitting devices arranged in arrays, rows, or other patterns, each light emitting device being configured to illuminate a particular symbol/pattern in one example. Each light emitting device may include a plurality of modular banks of LEDs which are configured to emit light through a clear lens within a particular field of view. The PDL arrays may provide visual feedback regarding the elevational and fore-aft position of the approaching aircraft relative to the boom envelope of the tanker aircraft.

BACKGROUND OF THE INVENTION

Pilot Director Lights (PDLs) generally consist of rows of lights mountedon the exterior of a refueling tanker aircraft for providing informationto the pilot of an approaching aircraft to prepare for and maintainrefueling boom engagement. Such lights may include lenses whose shapesor masking correspond to symbols or patterns to be illuminated to theapproaching pilot.

PDLs are used for providing positional and operational feedback in orderto help the approaching pilot prepare for and maintain contact betweenthe refueling boom nozzle and a fuel receptacle of the receivingaircraft. For example, PDLs may provide information as to theelevational (vertical), telescoping (fore-aft) and lateral (azimuthal)position of the approaching aircraft relative to the refueling tanker.Also, PDLs may provide operational information to the receivingaircraft's pilot regarding, for example, the progress of the refuelingprocess once the boom has been engaged.

FIG. 1 illustrates two light arrays used in conventional PDLs, which aremounted on a refueling tanker aircraft 10. Light array 22 is a row oflights that provide visual cues regarding the approaching aircraft'selevational position relative to an optimum position for refueling. Therow of lights in light array 24 provides visual information regardingthe approaching aircraft's fore-aft position relative to the optimumrefueling point. As shown in FIG. 1, light array 22 is positioned on theport side of the tanker's fuselage, while light array 24 is mounted onthe starboard side. Both arrays 22, 24 being located just forward of theleading edge of the wings.

FIG. 1 further shows that the symbols/patterns (arrows, rectangles,etc.) in light arrays 22 and 24 may illuminate at specific colors toprovide positional information. For example, as the receiver aircraftapproaches the refueling zone, the boom operator (aboard the tankeraircraft) may actuate signals through the PDLs to hold the receiveraircraft in the zone for the duration of the refueling operation. Whilein this zone, the lights indicate the progress of the operation alongwith signaling for any corrective maneuvers that the receiver pilot mustperform to remain engaged with the refueling boom.

In conventional PDLs, such as those shown in FIG. 1, incandescent lightbulbs may be used to illuminate the PDL symbols/patterns through tintedand diffused prismatic lenses. This results in various disadvantages.For example, the light being emitted from such PDLs may not be brightenough during daylight or fog conditions, due to losses incurred by thediffused and tinted lenses. Such losses also cause the PDLs to be veryinefficient (normally less than 1% efficient). This requires theincandescent light sources in conventional PDLs to be operated at a highwattage, thereby generating much heat and reducing the operational lifeof the light sources.

Furthermore, conventional PDLs are not very redundant. For example,conventional PDLs may utilize two bulbs to illuminate the letter “D” oflight array 22 in FIG. 1. It is possible, due to their short operationallife, that one or both of these bulbs may burn out while the refuelingtanker 10 is in the air, thus causing the “D” to be inadequatelyilluminated.

In addition, conventional PDLs, and even newer PDLs that use visiblelight emitting diodes (LEDs) as light sources are generally visible froma great distance at night. This is disadvantageous in situations whereaircraft need to operate at night without detection by the unaided humaneye.

SUMMARY OF THE INVENTION

According to an exemplary embodiment, the present invention is directedto Pilot Director Lights (PDLs) that selectively utilize visible orinfrared light emitting diodes (LEDs) as light sources. Each LED may beconfigured to illuminate light in a particular range of wavelengths, andto direct such light in a specific direction at a narrow angle.Furthermore, the LED light sources may be configured to dissipate a lowamount of power and generating less heat, as compared to incandescentlight sources.

Accordingly, the PDLs in exemplary embodiments of the present inventiondo not require tinted or prismatic lenses to generate light at aspecific color and in a specific direction. Thus, light may beilluminated at a higher efficiency. Also, the LED light sources mayprovide a longer operational life, resulting in less frequent burn-outsand replacements.

According to an exemplary embodiment, PDLs may be implemented as one ormore rows of light emitting devices, each device employing visible andinfrared LED light sources. Generally, the visible LEDs are used whenvisible operation is desired and the infrared LEDs are used when covertoperation is desired. Each light emitting device may correspond to aspecific symbol or pattern that provides positional or operationalinformation to the pilot of an approaching aircraft. Furthermore, LEDsmay be implemented in each light emitting device as modular banks. Thebanks of LEDs may be configured so that each bank may be replacedseparately, while other banks in the device remain in operation.

In another exemplary embodiment, the LEDs in each bank may be arrangedas subsets of visible or infrared LEDs, in which the LEDs of each subsetare connected in series, and the subsets of visible and infrared LEDs ofeach bank are connected in parallel with subsets containing the same LEDtype (visible or infrared). In such a series-parallel configuration, afault occurring within one subset of LEDs would not cause the othersubsets to fail.

According to an exemplary embodiment, each light emitting device iscomprised of a plurality of LED banks, each bank including multiplesubsets of LEDs, thereby providing a high degree of redundancy. As such,a burn-out of a single LED will only effect the operation of the subsetof LEDs to which it is connected, and therefore may not significantlyaffect the readability of the symbol or pattern being illuminated by thecorresponding light-emitting device.

An exemplary embodiment of the present invention includes a mountingstructure for mounting the light emitting devices of each row of PDLs tothe exterior of a refueling tanker's fuselage. Such a mounting structuremay include a hinged metal cover providing easy access for replacementof the LED banks. Furthermore, since tinted and prismatic lenses are notrequired, an optically clear lens may be integrated with the mountingstructure for each light emitting device.

In another exemplary embodiment of the present invention, a controlcircuit is implemented to control the operation of each light emittingdevice. Such a control circuit may be configured to control the currentflowing to the LED light sources of each light emitting device from acorresponding power supply. Furthermore, the control circuit may beconfigured to control a dimming operation of each light emitting device.The control circuit may also include an electromagnetic interferencefilter arranged between the power supply and the light emitting devices.

Further advances in scope of applicability of the present invention willbecome apparent from the detailed description provided hereinafter.However, it should be understood that the detailed description andspecific embodiments therein, while disclosing exemplary embodiments ofthe invention, are provided by way of illustration only.

BRIEF DESCRIPTION OF THE DRAWINGS

Preferred and alternative embodiments of the present invention aredescribed in detail below with reference to the following drawings:

FIG. 1 illustrates the positioning and configuration of conventionalPDLs on the exterior of a refueling tanker aircraft;

FIG. 2 illustrates a side view of PDLs mounted on the exterior of arefueling tanker aircraft, according to an exemplary embodiment of thepresent invention;

FIG. 3 illustrates an upward view of PDLs mounted on the exterior of arefueling tanker aircraft, according to an exemplary embodiment of thepresent invention.

FIGS. 4A and 4B illustrate a light emitting device for illuminating aparticular symbol, according to an exemplary embodiment of the presentinvention;

FIG. 5 illustrates a cross-sectional view of the light emitting devicein FIG. 2, according to an exemplary embodiment of the presentinvention;

FIGS. 6A and 6B illustrate a modular bank of visible and infrared lightemitting diodes (LEDs) implemented in a light emitting device, accordingto an exemplary embodiment of the present invention;

FIG. 7 illustrates an upward view of a boom envelope corresponding tothe refueling boom of a tanker aircraft used for refueling anapproaching aircraft, according to an exemplary embodiment of thepresent invention;

FIG. 8 illustrates a side view of a boom envelope corresponding to therefueling boom of a tanker aircraft used for refueling an approachingaircraft, according to an exemplary embodiment of the present invention;

FIG. 9 illustrates a block diagram of a control circuit configured tocontrol the current being supplied to the light emitting devices in aset of PDLs, according to an exemplary embodiment of the presentinvention; and

FIG. 10 illustrates a schematic diagram of the current control circuitof FIG. 9, according to an exemplary embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention is directed to dual mode Pilot Director Lights(PDLs) on the exterior of a refueling tanker aircraft, which selectivelyutilize visible and/or infrared light emitting diodes (LEDs) as a lightsource. Visible LEDs generally refer to LEDs that produce light visibleto the unaided human eye. FIGS. 2 and 3 illustrate a side view andupward view, respectively, of an example implementation of PDLs on theexterior of a refueling tanker aircraft 10 for use in conducting therefueling of an approaching aircraft 30. As shown in FIG. 10, the PDLsmay be implemented as two rows of lights 122 and 124, which are operableto illuminate symbols and patterns similar to those in light arrays 22and 24 illustrated in FIG. 1. For example, row 122 may be used forproviding information to the pilot of the approaching aircraft 30 as tothe elevational (vertical) position of aircraft 30 with respect to anoptimum position for performing the refueling operation. Also, row 124may be configured to provide fore-aft positioning information of theapproaching aircraft 30 in accordance with the optimum refuelingposition.

Referring to FIG. 2, the aircraft 30 attempts to position itselfrelative to the tanker aircraft 10 so that a refueling nozzle attachedto the end of boom 12 engages with a refueling receptacle 32 of aircraft30. As shown in FIG. 2, the boom 12 extends from a portal 18 on thetanker aircraft 10. Thus, boom envelope 14 shown in FIGS. 2 and 3illustrates a three-dimensional range of positions at which therefueling receptacle 32 of aircraft 30 may be properly engaged with thenozzle of boom 12 for refueling. The visual cues provided by PDL rows122 and 124 provide feedback to the pilot of aircraft 30 to adjust theaircraft's 30 relative position to place and maintain the receptacle 32in the boom envelope 14.

It should be noted that the boom envelope 14 may be defined as a rangeof lengths and vertical and azimuthal angles at which the boom 12extends in order to engage with receptacle 32.

According to an exemplary embodiment, each symbol (e.g., letter) orpattern (e.g., arrow or square) to be illuminated by the PDLs may beimplemented as one of an array or row of light emitting devices (e.g.,122 or 124), each light emitting device having its own LED light source.In one example, each light emitting device includes both visible andinfrared LED light sources that are selectively switchable between usingthe visible and the infrared LED light sources, with the infrared lightsources being used when covert operation is desired.

FIGS. 4A and 4B illustrate a light emitting device 200 according to anexemplary embodiment. Specifically, FIGS. 4A and 4B illustrate a lightemitting device 200 configured to illuminate the “D” implemented in row122 to provide elevation position feedback.

FIGS. 4A and 4B show that light emitting device 200 includes a lightsource, which is comprised of a plurality of modular banks of LEDs 210encased within a mounting structure. In an example embodiment, themodular banks of LEDs 210 include both visible and infrared LEDs. Themounting structure is comprised of a metal cover 240 and a clear lens230. The mounting structure is used for attaching the light emittingdevice to the exterior of the refueling tanker 10. In an exemplaryembodiment, the metal cover may have an aerodynamic shape as illustratedin FIGS. 4A and 4B.

According to an exemplary embodiment, the letter “D” may be created onlens 230 by a masking process. In such a process, a covering (e.g.,masking tape) in the shape of the letter “D” is placed over the lens230, and the uncovered portion of the lens 230 is painted. Thus, whenthe covering is removed, the unpainted portions of lens 230 will formthe letter “D.” This process may also include screen printing. It willbe readily apparent that the above-described masking process may be usedto create other symbols/patterns.

As shown in FIGS. 4A and 4B, the LED banks 210 may be positioned at aparticular angle with respect to the lens 230 to cause thelight-emitting device 200 to emit light at a particular field of viewdirected to the approaching aircraft 30. A more detailed description ofthe range and field of view corresponding to a light emitting device 200will be provided below in connection with FIGS. 6A-8.

FIG. 5 illustrates a cross-sectional view of a light emitting device200. FIG. 5 illustrates an aerodynamic shape for the metal cover 240,according to an exemplary embodiment. Furthermore, FIG. 5 illustrates amodular bank of LEDs 210, which is implemented in the light emittingdevice 200 at a particular angle with respect to the metal cover 240 andclear lens 230 (not shown).

FIGS. 6A and 6B provide a more detailed illustration of an example ofthe modular bank of LEDs 210 (sometimes referred to hereinafter as a“module”). As shown in FIGS. 6A and 6B, each module 210 includes a firstrow of visible LEDs 212 and a second row of infrared LEDs 214. In oneexample, each LED 212, 214 includes a narrow angle emitter 216, which isthe circular configuration at the end of the LED 212, 214 for emittinglight. According to an exemplary embodiment, each narrow angle emitter216 is configured to emit light that disperses at a relatively narrowangle, e.g., an angle of 30 degrees or less. Such narrow angle emitters216, and their principle of operation, are well known to those ofordinary skill in the art. In one example, the infrared LEDs 214 have awavelength of approximately 850 nanometers, and are operable throughouta temperature range of at least −55° C. to +75° C. Infrared LEDs, suchas those available from Epitex, Inc. or Osram, Inc. are used in anexample embodiment. The infrared LEDs 214 are compatible with nightvision imaging systems (NVIS), and the light produced from them may beseen using specialized goggles, for example.

As will be described below in more detail, the relatively low angle ofdispersion of light emitted by the narrow angle emitters 216 may beinstrumental in determining the field of view through which light isilluminated by the corresponding light emitting device 210.

Referring to FIGS. 6A and 6B, each module 210 includes multiple rows ofLEDs. Although the rows are shown to be the first row of visible LEDs212 and the second row of infrared LEDs in this example, otherconfigurations may be used in other embodiments. For example, each rowmay include an alternating pattern of visible and infrared LEDs or someother pattern of visible and infrared LEDs. Additionally, in otherembodiments, modules that include all visible and all infrared LEDsrather than a row of each may be used in alternating or other patterns.In still other embodiments, differing numbers of rows, such as two rowsof visible LEDs followed by two rows of infrared LEDs, may be used ineach module. Further, each row of LEDs 212, 214 may include aseries-parallel connection. According to such an embodiment, the LEDs212, 214 of each row are arranged in subsets, each subset comprising aplurality of LEDs 212 or 214 connected in series. The serially connectedsubsets of LEDs 212 and 214 within a row are then connected in parallelwith respect to other subsets of serially connected LEDs 212 and 214,such that serially connected subsets of visible LEDs 212 are connectedin parallel with other serially connected subsets of visible LEDs 212and serially connected subsets of infrared LEDs 214 are connected inparallel with other serially connected subsets of infrared LEDs 214.

Based on the series-parallel connections, when a fault occurs in onesubset, e.g., one of the LEDs 212, 214 fails, only the other LEDs 212,214 within the same serially connected subset are affected. Thus, whenone LED 212, 214 burns out, only the LEDs 212, 214 in the same subsetmay be lost; the LEDs 212, 214 in the other subsets may continueoperating normally.

According to an exemplary embodiment, the configuration of each module210 in a light emitting device 200 may include a first row of visibleLEDs 212 and a second row of infrared LEDs 214, where each row includestwelve LEDs 212 or 214 respectively. Such a configuration provides ahigh luminance-power efficiency, based on the current-drivencharacteristics of the LEDs 212, 214.

Furthermore, if the visible LEDs 212 within a module 210 are configuredto emit red or amber light, the twelve LEDs 212 within the row ofvisible LEDs 212 may be arranged in two subsets of six series-connectedLEDs 212. On the other hand, if the LEDs 212 emit white or green light,the twelve LEDs 212 in the row may be arranged in three subsets, eachsubset containing four LEDs 212 connected in series. Such an arrangementfurther provides high efficiency. Rows containing infrared LEDs 214 maybe connected in similar fashions.

Such a configuration may provide each light emitting device 200 with ahigh amount of redundancy, in order to ensure that the correspondingsymbol or pattern will be illuminated despite a burn-out in any of theLEDs 212, 214. For example, a light emitting device 200 that illuminatesthe letter “D” may include eleven modules 210, thereby including 264combined visible and invisible LEDs 212, 214. Such an embodimentprovides much more protection against light source failure than aconventional PDL, for example, which utilizes two incandescent bulbs toilluminate “D.”

Such light emitting devices 200, as described in the above embodiments,dissipates a low amount of power and generates little heat while inoperation. Therefore, it is possible in exemplary embodiments to replaceone of the modules 210 of a light emitting device 200 while the othermodules are in operation and turned on. This provides advantages overconventional systems, in which the replacement of a light source in thePDLs require the other light sources to turn off and cool down beforesuch replacement is performed.

It should further be noted that the low amount of power dissipation andheat generation allows the LEDs 212, 214 in the light emitting devices200 to have a long operation life, thus requiring replacement much lessfrequently.

According to an exemplary embodiment, the above-described configurationof the light emitting devices 200 in a PDL system allows a perceiveduniform sheet of visible or infrared light to be emitted through thelens 230 to the pilot of an approaching aircraft 30, while the pilot isin a particular field of view of the light emitting device 200.According to an exemplary embodiment, this field of view corresponds tothe approaching pilot's location when the fuel receptacle 32 of aircraft30 is in alignment with the boom envelope 14 (i.e., the receptacle 32 islined up to receive the nozzle of the boom 12 from the refueling tankeraircraft 10).

In an exemplary embodiment, the configuration of LEDs 212, 214 in alight emitting device 200 will cause the emitted sheet of light tostriate as the pilot of the approaching aircraft 30 moves out of thefield of view. In other words, the light emitted from at least one ofthe light emitting devices 200 striates as the approaching aircraft 30moves such that the fuel receptacle 32 moves out of alignment with theboom envelope 14. Accordingly, the pilot of aircraft 30 may be notifiedby the progressive striation of the emitted light of one or more of thelight emitting devices 200 that he/she is falling off course and needsto correct the aircraft's 30 position with respect to tanker aircraft10. Thus, the striation of the light emitted from the light emittingdevice 200 provides “passive” positional feedback. The light is visiblelight from visible LEDs 212 when visible operation has been selected andthe light is infrared light from infrared LEDs 214 when covert operationhas been selected. In other words, the position of the approachingaircraft 30 need not be actively sensed/detected at the refueling tankeraircraft 10, in order to provide this feedback to the approaching pilot.

Furthermore, the progressive striation of the light pattern emitted fromthe light emitting device 200 may provide an indication to the pilot ofthe speed at which the approaching aircraft 30 is falling off course.

The striation of emitted light may be dependent upon the angle ofdispersion of the narrow angle emitters 216 along with the relativespacing of the LEDs 212, 214. Those of ordinary skill in the art willrealize how such factors can be manipulated in order to cause thedesired striation effect for a light emitting device 200.

FIGS. 7 and 8 illustrate a relationship between the boom envelope 14 andthe field of view corresponding to at least one of the light emittingdevices 200, according to an exemplary embodiment. As shown in FIGS. 7and 8, the approaching aircraft 30 attempts to position itself inrelation to tanker aircraft 10 so that the boom 12 will engage with thefuel receptacle 32 at a point P within the boom envelope 14.

FIG. 7 illustrates an upward view of the three-dimensional boom envelope14, while FIG. 8 illustrates a side view of the boom envelope 14. Thesefigures show an axis 16 through the center of the refueling tankeraircraft 10. As shown in FIG. 7, the boom envelope 14 has an azimuthalrange from +A₁ to −A₂ degrees with respect to axis 16 (using boom portal18 as an originating point). FIG. 8 shows that the range of elevationalangles of boom envelope 14 is from −E₁ to −E₂ degrees with respect to aline parallel with axis 16 (where portal 18 is an originating point).

Therefore, as long as the fuel receptacle 32 of aircraft 30 remainslined up with any point P within the boom envelope 14, the light emittedfrom at least one of the light emitting devices 200 will appear as asheet of light to the approaching pilot. For example, when using thevisible LEDs 212, one of light emitting devices 200 in the elevationalrow of PDLs 122 may illuminate a solid sheet of green light (similar tothe green square of array 22 in FIG. 1) when the fuel receptacle 32 isaligned with the boom envelope 14. However, as the elevational positionof receptacle 32 moves outside of alignment with boom envelope 14,horizontal striations may appear in this sheet of green light.Furthermore, as the lateral (azimuthal) position of receptacle 32 movesout of alignment with boom envelope 14, vertical striations may appearin each of the symbols/patterns illuminated by row 122 to theapproaching pilot. When using the infrared LEDs 214, solid and striatedsheets of infrared light would be produced in a similar fashion to thatdescribed with respect to the green light when using visible LEDs.

Also, based on the configuration (e.g., the relative positions andnarrow angle emitters 216) of the LEDs 212, 214, the light from a lightemitting device 200 may be emitted within a limited range, striated ornot. For example, FIG. 7 illustrates an azimuthal range of illuminationof +15 degrees to −15 degrees with respect to axis 16. Furthermore, FIG.8 shows an elevational range of −5 to −20 degrees with respect to a lineparallel with axis 16 (using the light emitting device 200 as anoriginating point). When the fuel receptacle 32 is no longer alignedwithin these two ranges, the pilot of aircraft 30 may no longer be ableto see the light being emitted by the corresponding light emittingdevice 200.

The limited range of illumination in such embodiments may provide theapproaching pilot passive feedback as to how far the aircraft 30 hasgone off course. Also, the limited range of illumination in suchembodiments may allow the refueling operation to be performed somewhatcovertly with respect to surrounding aircraft and ground stations evenwhen visible LEDs 212 are used. This may be useful, e.g., duringmilitary operations where covertness is desired. However, use of theinfrared LEDs 214 rather than the visible LEDs 212 allows a greaterlevel of covert operation because the infrared LEDs 214 are generallynot visible to the unaided human eye.

It should be noted that the limited range of illumination for a lightemitting device 200 may be a function of other factors in addition tothe narrow angle emitters 216 of LEDs 212, 214. For example, the angularpositioning of the modules 210, the geometry and curvature of metalcover 240, the shape and dimensions of clear lens 230, or a combinationof such factors may be used to achieve a desired range of illumination,as will be readily understood by those of ordinary skill in the art.

As described in the above embodiments, the PDLs of the present inventionmay direct light to a particular field of view, and utilize passivefeedback such as striated light, without the need of prismatic ordiffused lenses or other such devices. In exemplary embodiments, clearlenses (or no lens at all) may be used. Thus, the losses of luminancecaused by the use of diffused and prismatic lenses may be avoided.

Since the light source of each light emitting device 200 is comprised ofcurrent-driven components (LEDs 212, 214), exemplary embodiments of thepresent invention include a control circuit for controlling the currentbeing supplied to each light emitting device 200 by a power source. FIG.9 illustrates a block diagram of such control circuitry (referred tohereinafter as “current control device”) for a particular light emittingdevice 200.

As shown in FIG. 9, a current control device 300 includes a controldevice 310 and an electromagnetic (EMI) filter 320 implemented between aDC power supply (e.g., +28 VDC) and the light emitting device 200. Inparticular, EMI filter 320 includes circuitry whose configuration andoperation is well-known to those of ordinary skill in the art forfiltering out the EMI effects of the input DC power supply. The EMIfilter 320 helps protect the operation of the corresponding lightemitting device 200 from being interrupted by such effects, andprohibits the PDL system from inducing interference into surroundingelectronics. Additionally, each current control device 300 (orcomponents therein) may be encased in a metallic structure equipped withEMI filtered connectors. In an example embodiment, power from thecurrent control device 300 supplied to the visible LEDs 212 when the PDLis in a standard, visible mode and power is supplied to the infraredLEDs 214 when the PDL is in a covert mode. This may be done usingswitches (not shown) that selectively connect the power to either thevisible LEDs 212 or the infrared LEDs 214 based on a control signalreceived from a human operator or a computer system. Alternatively, inother embodiments, multiple current control devices 300 may be used insuch a way that any one particular current control device 300 providespower only to visible LEDs 212 or infrared LEDs 214, and provides suchpower only when the appropriate mode (standard visible or covert) hasbeen selected.

The output of EMI filter 320 is supplied to a power supply interface 312within control device 310. Power supply interface 312 generates amodular supply voltage (e.g., +15 VDC) to be distributed to each LEDmodule 210 in the light emitting device 200. The power supply interfacemay also generate dimming supply voltages (e.g. ±5 VDC) to be sent to adimming control device 313. Power supply interface 312 also includescircuitry that provides reverse polarity protection for the dimmingcontrol device 313 and light emitting device 200.

According to an exemplary embodiment, the dimming control device 313utilizes pulse width modulation (PWM) to conduct a dimming operation onthe LEDs 212 or 214 of the light emitting device 200. In particular,dimming control device 313 includes a dimming signal converter 316 forreceiving a dimming control signal Dim (e.g., between 0-5 V). A PWMoutput unit 318 receives the converted analog voltage from dimmingsignal converter 316 as well as a signal generated by PWM ramp generator314 in order to output a modulated square wave signal. The duty cycle ofthis square wave PWM output signal is dependent upon the magnitude ofthe analog signal generated by the dimming signal converter 316. The PWMoutput signal thus controls the level at which the LEDs 212, 214 oflight emitting device 200 is illuminated. In an example embodiment, thedimming control device 313 is used during covert operation mode tosupply a first output signal to the infrared LEDs 214 that results inthe LEDs having a predetermined low brightness level to provide symboland shape definition and a second output signal to selected infraredLEDs 214 that results in the selected LEDs 214 having a predeterminedhigher brightness level than those to which the first output signal isbeing supplied by the dimming control device 313.

Various circuit arrangements and configurations may be utilized toimplement the components of control device 310, as will be readilyapparent to those of ordinary skill in the art.

FIG. 10 is a schematic diagram illustrating an example implementation ofthe various components of the current control device 300 of FIG. 9,according to an exemplary embodiment. It should be noted however thatFIG. 10 is provided for purposes of illustration, and should not beconstrued as limiting the configuration and components of the currentcontrol device 300 of the present invention.

The connections of the power supply and dimming control in FIG. 10 areas follows. The DC power supply (e.g., +28 VDC) and return are connectedto terminals E1 and E2. Terminal E3 is connected to ground. The dimmingsignal Dim and return are connected to terminals E4 and E5. Terminals E6and E7 output the supply voltage (e.g., +15 V) and the PWM outputsignal, respectively, to the LED banks 210.

The components of FIG. 10 are implemented in the functional componentsof FIG. 9 as follows. The configuration including inductors L1-L4 andcapacitors C1-C3 comprise the EMI filter 320. The configuration of FIG.10 including power converter U1, capacitors C4-C8, inductors L4, diodeD3, and voltage regulator U2 corresponds to the power supply interface312. The PWM ramp generator 314 includes the configuration of op ampsU3:A and U3:B, and capacitors C9 and C10 in FIG. 10. The dimming signalconverter 316 corresponds to the configuration in FIG. 10 includingdiodes VR1 and VR2, capacitors C11-C13 and amplifier U3:C. The PWMoutput unit 318 is illustrated in FIG. 10 as the configuration includingamplifier U3:D, capacitors C14 and C15, transistor Q1, and diode VR3.Those of ordinary skill in the art will appreciate the principles ofoperation and the various means of implementation of the circuitconfiguration illustrated in FIG. 10.

According to an exemplary embodiment, the dimming control device may becontrolled manually by the boom operator on the tanker aircraft 10, orautomatically by devices/computers in the aircraft 10. The dimmingcontrol device 313 may be used to dim the LEDs 212, 214 of a lightemitting device 200 in order to provide visual feedback to the pilot ofan approaching aircraft 30. For example, the luminance of a PDL may beset higher for daylight or low visibility conditions (e.g., cloud cover,precipitation, etc.), set lower for night operations, or use varyingbrightness levels when the infrared LEDs 214 are used. Selection of thestandard mode using the visible LEDs 212 or the covert mode using theinfrared LEDs 214 also may be controlled manually by the boom operatoron the tanker aircraft 10, or automatically by devices/computers in theaircraft 10 in an example embodiment. Additionally, in an exampleembodiment, the pilot of the approaching aircraft 30 ordevices/computers in the approaching aircraft 30 may send requests tothe tanker aircraft 10 indicating whether manual or automatic operationis desired, as well as whether standard or covert mode should be used.

In an exemplary embodiment, the dimming operation may be performed atnight, to ensure that the light from the light emitting device 200 isnot too bright. This may improve readability for the approaching pilotand increase the covertness of the refueling operation.

While the PDLs in the above exemplary embodiments are described asproviding elevational and fore-aft positional feedback to the pilot ofan approaching aircraft 30, it should be noted that other types ofinformation can be conveyed using the present invention. For example,the light emitting devices 200 of the present invention may be used toprovide feedback as to the status of the refueling operation after therefueling boom 12 has been engaged with the fuel receptacle 32.Furthermore, a light emitting device 200 may be used to notify theapproaching pilot that boom engagement has been made.

Also, the PDLs of the present invention may be used to help direct theapproaching aircraft 30 to a position P before boom engagement is made,and to assist the pilot in keeping the aircraft 30 within an acceptableposition after boom engagement has been made.

While the preferred embodiment of the invention has been illustrated anddescribed, as noted above, many changes can be made without departingfrom the spirit and scope of the invention. For example, both visibleand infrared LEDs may be used at the same time in some operationalmodes, rather than using exclusively visible or exclusively infraredLEDs. Accordingly, the scope of the invention is not limited by thedisclosure of the preferred embodiment. Instead, the invention should bedetermined entirely by reference to the claims that follow.

1. A dual mode pilot director light (PDL) apparatus mounted on arefueling tanker aircraft for directing a pilot in an approachingaircraft, the apparatus comprising: one or more light emitting devices,each including a first visible light emitting diode (LED) light sourceand a second infrared (IR) LED light source, at least one light emittingdevice emitting a light pattern that provides positional feedback to thepilot in the approaching aircraft, wherein the pilot's perception of thelight pattern changes as the approaching aircraft's relative positionfalls off course with respect to at least one of an azimuthal andelevational range corresponding to the refueling aircraft's boomenvelope, such that the change in perception indicates to the pilot thatthe approaching aircraft has fallen off course, and wherein the lightemitting devices are controllable to selectively use either the firstLED light source in a standard mode or the second LED light source in acovert mode.
 2. The apparatus of claim 1, further comprising: a clearlens covering each of the light emitting devices.
 3. The apparatus ofclaim 1, wherein each light emitting device is operable to illuminate asymbol.
 4. The apparatus of claim 3, wherein when the covert mode isselected, the IR LED light source operates at a predetermined low levelbrightness level when inactive and at a predetermined higher brightnesslevel when active.
 5. The apparatus of claim 1, the light emittingdevices being arranged into first and second assembly strips to providepositional feedback to the pilot, the light emitting devices in thefirst assembly strip are configured to provide feedback regardingfore-aft positioning of the approaching aircraft, and the light emittingdevices in the second assembly strip are configured to provide feedbackregarding elevation positioning of the approaching aircraft.
 6. Theapparatus of claim 1, wherein each light emitting device is configuredto illuminate a symbol or direction for providing at least one ofpositional and operational feedback with respect to a refuelingoperation being performed on the approaching aircraft.
 7. The apparatusof claim 1, wherein at least one of the light emitting devices isconfigured to emit a sheet of light, through a corresponding lens, tothe pilot when a fuel receptacle of the approaching aircraft is alignedwith a boom envelope associated with the refueling tanker aircraft.
 8. Adual mode pilot director light (PDL) apparatus mounted on a refuelingtanker aircraft for directing a pilot in an approaching aircraft, theapparatus comprising: one or more light emitting devices, each includinga first visible light emitting diode (LED) light source and a secondinfrared (IR) LED light source, wherein the light emitting devices arecontrollable to selectively use either the first LED light source in astandard mode or the second LED light source in a covert mode, whereinat least one of the light emitting devices is configured to emit a sheetof light, through a corresponding lens, to the pilot when a fuelreceptacle of the approaching aircraft is aligned with a boom envelopeassociated with the refueling tanker aircraft, and wherein the at leastone of the light emitting devices is configured so that the emittedsheet of light striates as the fuel receptacle moves out of alignmentwith the boom envelope.
 9. A dual mode pilot director light (PDL)apparatus mounted on a refueling tanker aircraft for directing a pilotin an approaching aircraft, the apparatus comprising: one or more lightemitting devices, each including a first visible light emitting diode(LED) light source and a second infrared (IR) LED light source, at leastone light emitting device emitting a light pattern that providespositional feedback to the pilot in the approaching aircraft, whereinthe pilot's perception of the light pattern changes as the approachingaircraft's relative position changes, thereby providing the positionalfeedback to the pilot, and wherein the LED light source of at least oneof the light emitting devices includes one or more modules of LEDs, eachof the LEDs including a narrow angle emitter for emitting light, andwherein the light emitting devices are controllable to selectively useeither the first LED light source in a standard mode or the second LEDlight source in a covert mode.
 10. The apparatus of claim 9, wherein thenarrow angle emitter is configured to emit light, which dispersessubstantially at an angle of 30 degrees.
 11. The apparatus of claim 9,further comprising a mounting structure for each of the light emittingdevices, each mounting structure including, a hinged metal cover havingopenings corresponding to each module; and a clear lens covering eachopening, wherein the metal cover is configured so that each openingprovides a range of illumination through the corresponding clear lens.12. The apparatus of claim 11, wherein the range of illuminationincludes an elevational range of substantially −5 and −20 degrees, andan azimuthal range of substantially +15 and −15 degrees, with respect toa longitudinal axis of the refueling tanker aircraft.
 13. The apparatusof claim 9, wherein each module includes multiple rows of LEDs arrangedin subsets, each subset includes one or more LEDs connected in series,and at least two subsets of each row are connected in parallel.
 14. Theapparatus of claim 13, wherein each subset of the module is electricallyisolated from faults occurring with respect to other subsets in themodule.
 15. The apparatus of claim 13, wherein each module includes 2rows of LEDs, each row including 12 LEDs, and each row is configured toinclude at least one of: 2 subsets of 6 LEDs, and 3 subsets of 4 LEDs.16. The apparatus of claim 13, wherein each light emitting device isconfigured so that any module can be replaced while other modules in thelight emitting device are in operation.
 17. The apparatus of claim 9,wherein each module can be replaced while other modules are inoperation.
 18. The apparatus of claim 9, further comprising: a currentcontrol device configured to control the current supplied to each lightemitting device.
 19. The apparatus of claim 18, wherein the currentcontrol device includes, a dimming control device configured to utilizepulse width modulation (PWM) to conduct dimming of the LEDs in the lightemitting device; and a power supply interface operably connected to apower supply, the power supply interface being configured to generatesupply voltages and provide reverse polarity protection for the dimmingcontrol device and the light emitting device.
 20. The apparatus of claim1, wherein the positional feedback is provided to the pilot withoutrequiring a determination at the refueling tanker aircraft of theapproaching aircraft's relative position.